P. Novák, J. Šimek, and J. Kostelecký. Gravity and Geoid 2002. Reviewed Proc. of the 3rd Meeting of the International Gravity and Geoid Commission, page 150--155. (2003)
E. Grafarend, and A. Ardalan. Final Results of the Baltic Sea Level 1997 GPS Campaign, Report 99:4, The Finnish Institute of Geodesy, Kirkonummi, (1999)